Cleaning Method

ABSTRACT

This invention relates to a method of softening water and/or in which the deposition of hard water scale is inhibited. The invention relates in particular to such a method carried out in a domestic environment, in particular in ware-washing machines. A compressed water-softening composition comprising a water softening active and a blend of disintegrating agents, comprising a cross-linked polyplasdone, a water-swellable cellulose and optionally a water soluble salt is claimed.

This invention relates to a method of softening water and/or in whichthe deposition of hard water scale is inhibited. The invention relatesin particular to such a method carried out in a domestic environment, inparticular in ware-washing machines. The invention also relates tocompressed water-softening compositions for such methods.

It is well known that certain metal compounds, notably calciumcompounds, when present in water, have a significant effect on theproperties of the water. For example, “hard” water containing asignificant loading of soluble calcium and magnesium compounds mayrequire a large amount of soap or detergent in order to form a lather.Scale deposits can readily form from such water, for example on heatingor pH change or evaporation. These can be encrustations, or watermarksleft on evaporation of water droplets from, especially, a shiny surface.

There have been many proposals for removal of metal ions from aqueoussolutions. In the industrial context proposals have included filter bedsand polymeric filters for capturing heavy metal ions from an aqueoussolution flowing within a passageway. Examples are given in EP992238Aand GB20869564A. In the domestic context chelating compositions can beadded to an aqueous washing solution and these can capture metal ions,such as calcium ions. Examples of chelating compositions are given inEP892040A.

Increasingly popular is the delivery of cleaning and water-softeningcompositions as compressed compositions, typically a tablet. These areconvenient, providing a unit dosage which is easily handled.Difficulties arise in the production of such compressed compositions inbalancing the needs that the compressed composition is suitably hard andnon-friable under transportation conditions but yet is not so compactedthat it cannot easily disintegrate. Suitable levels of “hardness” arebetween 150 N and 250 N (the test conditions being set out in theExample section). Suitable levels of “friability” are between 2% and 9%(the test conditions being set out in the Example section). Suitable“disintegration” times are between 5 seconds and 180 seconds, whenplaced in 11 of gently stirred water at 25° C.

It is well known in the art to include a disintegrant, which willpromote disintegration of the tablet in laundry detergent tablets andlaundry detergent additive tablets. Various classes of disintegrants areknown, including the class in which disintegration is caused by theswelling of the disintegrant. Various swelling disintegrants have beenproposed in the literature, for instance in WO 98/54283, with thepreference being directed predominantly towards starches, celluloses andwater soluble organic polymers. Furthermore, inorganic swellingdisintegrants such as bentonite clay have also been mentioned, forinstance in EP-A-0466 484.

We have found that water-softening compositions are particularlydifficult compositions to compress and retain as a compressed solid.This is mainly due to the high content of crystalline solids (ascompared to detergent tablets that contain higher amounts of organicmolecules, such as surfactant), for example, citrate salts andsilicates, that do not easily bind together. Therefore, much highercompression forces are needed to produce suitable compressedcompositions. Compression forces used are greater than 35 KN, 40 KN, 45KN or 50 KN. However, compression forces are usually less than 100 KU,95 KN, 90 KN, or 85 KN.

We have found a particularly suitable water softening composition forthe formation of a compressed composition that provides high levels ofhardness of at least 100 N, 150 N, 175 N or 200 N. Hardness levels areusually less than 300 N, 275 N or 250 N. An acceptably low lend offriability of less than 15%, 10% or 8%. Low disintegration times of lessthan 1 minute are achieved ideally between 20 and 30 seconds.

EP 0812808 discloses water-softening tablets containing disintegrants.

Therefore, we present as a first feature of the invention a compressedwater softening composition comprising at least one water-softeningactive and a blend of disintegrating agents comprising

-   -   (a) cross linked polyplasdone;    -   (b) a water-swellable cellulose; and, optionally,    -   (c) a water-soluble salt.

By the use of the term water-softening composition we mean that thecomposition is substantially free of surfactant and/or bleachingredients, i.e. less than 5% or 1% by weight, ideally 0% by weight.

As discussed above, water softening compositions are characterised inthat they contain large amounts of water softening active ingredientsthat are crystalline material, i.e. more than 35% by weight, more than38% by weight, more than 40% by weight or more than 42% by weight.

Typical crystalline materials include citrate sales, zeolites, silicatesand clays. Preferably such crystalline materials are selected fromcitrate salts or silicate.

The blend of disintegrating agents is present in an amount of up to 10%,8%, 7%, 6%, 5%, 3% or 2% wt of the composition. The blend ofdisintegrating agents is present in an amount of at least 0.1%, 0.3%,0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5% or 1.7% wt of the composition.

Water Softening Active

Water-softening actives are present in the composition in an amount ofat least 40%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90% by weight ofthe composition. Maximum amounts of water-softening actives are presentin an amount of less than 99%, 97%, 93%, 90%, 87%, 83% or 80% by weightof the composition.

There are three main types of method of action for water softeningactives, described below.

1) Ion exchange agents—such agents include alkali metal (preferablysodium) aluminosilicates either crystalline, amorphous or a mixture ofthe two. Such aluminosilicates generally have a calcium ion exchangecapacity of at least 50 mg CaO per gram of aluminosilicate, comply witha general formula:

0.8-1.5 Na₂O.Al₂O₃.0.8-6 SiO₂

and incorporate some water. Preferred sodium aluminosilicates within theabove formula contain 1.5-3.0 SiO₂ units. Both amorphous and crystallinealuminosilicates can be prepared by reaction between sodium silicate andsodium aluminate, as amply described in the literature.

Suitable crystalline sodium aluminosilicate ion-exchange detergencybuilders are described, for example, in GB 1429143 (Procter & Gamble).The preferred sodium aluminosilicates of this type are the well knowncommercially available zeolites A and X, and mixtures thereof. Also ofinterest is zeolite P described in EP 384070 (Unilever).

Another class of compounds are the layered sodium silicate builders,such as are disclosed in US-A-4464839 and US-A-4820439 and also referredto in EP-A-551375.

These materials are defined in US-A-4820439 as being crystallinelayered, sodium silicate of the general formula

NaMSi_(x)O_(2x+).YH₂O

where

M denotes sodium or hydrogen,

x is from 1.9 to 4 and y is from 0 to 20.

Quoted literature references describing the preparation of suchmaterials include Glastechn. Ber. 37,194-200 (1964), Zeitschrift furKristallogr. 129, 396-404 (1969), Bull. Soc. Franc. Min. Crist., 95,371-382 (1972) and Amer. Mineral, 62, 763-771 (1977). These materialsalso function to remove calcium and magnesium ions from water, alsocovered are salts of zinc which have also been shown to be effectivewater softening agents.

2) Ion capture agents—agents which prevent metal ions from forminginsoluble salts or reacting with surfactants, such as polyphosphate,monomeric polycarbonates, such as citric acid or salts thereof, EDTA,algins, alginates.

3) Anti-nucleating agents—agents which prevent seed crystal growth, suchas polycarbonate polymers, such as polyacrylates, acrylic/maleiccopolymers, and acrylic phosphonates, and sulfonates.

Water-Soluble Salt

The water-soluble salt is an optional, but preferred, constituent of thedisintegrant blend. Ideally it is present in amounts of up to 0.1%possibly up to 0.2, 0.4, 0.6, 0.8. 1.0, 1.2 or 1.4% by weight of thecomposition. Ideally the water-soluble salt is provided as at least 5%,10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%,80% or 85% by weight of the disintegrant blend. Ideally thewater-soluble salt is provided as no more than 95%, 90%, 85%, 80%, 75%,70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15% or 10% byweight of the disintegrant blend.

Ideally the water-soluble salt has a solubility of at least 50 g/100 gin deionized water at 20° C. This is an exceptionally high solubility:many materials which are classified as water-soluble are less soluble.Suitable highly water-soluble materials which may be used are selectedfrom, with their solubilities expressed as grams of solid to form asaturated solution in 100 g of deionized water at 20°C.: potassiumacetate >200, potassium carbonate 112, urea >100, sodium acetateanhydrous 119, sodium acetate trihydrate 76 and magnesium sulphate. 7H2O71 or mixtures thereof.

The rapid dissolution of the water-soluble salt provides rapid ingressof water into the tablet, thus not only affecting the tablet'sintegrity, but allowing water to rapidly access the other disintegrantcomponents within the tablet, particularly the swelling disintegrants.

By contrast the solubilities of some other common materials at 20° C.are: sodium chloride 36, sodium sulphate decahydrate 21.5, sodiumcarbonate anhydrous 6.0, sodium percarbonate anhydrous 12, sodiumperborate anhydrous. Preferably this highly water soluble material isincorporated as particles of the material in a substantially pure form(i.e. each such particle contains over 95% by weight of the material).

Cross Linked Polyplasdone

Ideally present in the composition in amounts of up to 0.1% possibly upto 0.2, 0.4, 0.6, 0.8. 1.0, 1.2 or 1.4% by weight of the composition.Ideally the cross linked polyplasdone is provided as at least 5%, 10%,15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or85% by weight of the disintegrant blend. Ideally the cross linkedpolyplasdone is provided as no more than 95%, 90%, 85%, 80%, 75%, 70%,65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15% or 10% by weightof the disintegrant blend.

Cross linked polyplasdone consists of N-vinyl-2-pyrrolidone polymerisedand cross-linked simultaneously by a reaction known as “pop-corn”polymerisation. The unique structure of cross linked polyplasdone(sometimes referred to as crospovidone) provides superior adsorptivecapacity and exceptional swelling rate. Suitable methods for preparingcross linked polyplasdone can be found in EP 1263814 & EP 1036839.

Water-Swellable Cellulose

Ideally present in the composition in amounts of up to 0.1% possibly upto 0.2, 0.4, 0.6, 0.8. 1.0, 1.2 or 1.4% by weight of the composition.Ideally the water-swellable cellulose is provided as at least 5%, 10%,15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or85% by weight of the disintegrant blend. Ideally the water-swellablecellulose is provided as no more than 95%, 90%, 85%, 80%, 75%, 70%, 65%,60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15% or 10% by weight of thedisintegrant blend.

Suitable water-swellable cellulose materials have sufficientwater-absorptivity that they can absorb at least 15, 12, 10, 8, 6, 4, 2,1 times their own weight of water, ie. a water uptake of at least 15,12, 10, 8, 6, 4, 2, 1 g per g of deionised water at 20° C.

A number of such materials are known, and which may be chemicallymodified to enhance its water uptake capacity. Sometimes such modifiedcelluloses have ionic substituents but for this invention it ispreferred that any substituents are nonionic.

For the avoidance of doubt water-swellable cellulose does not includemicrocrystalline cellulose commonly used in compacted compositions.Microcrystalline cellulose is used as a wicking agent to bring waterinto the compacted composition to aid disintegration and is notwater-swellable, or at least is not water-swellable to the extentrequired in the present invention. Microcrystalline cellulose may beincluded as an additional disintegrant.

The compositions may be used in ware washing using a machine or a manualmethod. The compositions may also be used to soften water in othercleaning methods such as hard surfaces, for example using a hand-clothor mop, and an open vessel, for example a bucket or bowl. Thus, thecleaning method could be a method of cleaning a hard surface, forexample a window, a tiled surface, shower screen, dirty tableware andkitchenware, a sanitary article, for example a bath, shower screen,lavatory, wash basin or sink, a car or a kitchen worktop.

The invention will now be described, by way of embodiment, withreference to the following Examples.

EXAMPLES

Hardness Test

Using a dynamometer with a test piston diameter of 8 mm and a pistonspeed 30 mm per minute (a machine such as the ERWEKA tablet hardnesstester THB 30 may be used) the maximum hardness of the tablet just priorto breakage is recorded for 4 tablets in the same orientation andaveraged.

Friability Test

Ten tablets are weighed and placed into a square plastic sample holderof approximate dimensions 110×100 mm square by 170 mm long. The sampleholder is rotated horizontally along it length at 50 rpm for 1 minute.The tablets are weighed again and the amount of material loss expressedas percentage

${\% \mspace{14mu} {friability}\mspace{14mu} {index}} = {\frac{W_{0} - W_{1}}{W_{0}} \times 100}$

where:

-   -   W₀=initial weight    -   W₁=weight of the tablets after one minute of test at 50 rpm.

The tablets were pressed at between 50 and 80 N. The hardness wasmeasured at between 180 and 260 N, the friability was AROUND 4% anddissolution times of between 20 and 30 seconds were found.

1st 2nd Raw Materials % wt region region Total Water softening 26.00035.000 27.800 Homopolymer Citrate 60.500 46.000 57.600 PEG 4.500 4.0004.400 Polyplasdone + Cellulose 9.000 9.500 9.100 Dye 0.016 0.003 Filler5.484 1.097 TOTAL 100 100 100

1. A compressed water-softening composition comprising at least onewater-softening active and a blend of disintegrating agents comprising,a cross linked polyplasdone; a water swellable cellulose and, optionallya water soluble salt.
 2. A compressed water-softening composition asclaimed in claim 1 wherein the composition is substantially free ofsurfactant or bleach ingredients.
 3. A compressed water-softeningcomposition according to in claim 1 wherein the blend of disintegratingagents is present in an amount of up to 10% by weight of thecomposition.
 4. A compressed water-softening composition according toclaim 3 wherein the blend of disintegrating agents is present in anamount of at least 0.1% by weight of the composition.
 5. A compressedwater-softening composition according to claim 1 wherein thewater-soluble salt has a solubility of at least 50 g/100 g of deionisedwater at 20° C.
 6. A compressed water-softening composition according toclaim 1 wherein the water-swellable cellulose has a water uptake of atleast 15 g of deionised water at 20° C. per g of water-swellablecellulose.
 7. A compressed water-softening composition according toclaim 1 wherein the water-softening active is selected from the group:ion exchange agents, ion capture agents, and anti-nucleating agents. 8.A compressed water-softening composition according to claim 1 whereinthe cross linked polyplasdone is present in an amount of up to 1.4% wt.of the said composition.
 9. A compressed water-softening compositionaccording to claim 1 wherein the cross linked polyplasdone is present inan amount of up to 95% wt. of the blend of disintegrating agents.
 10. Acompressed water-softening composition according to claim 1 wherein thewater-swellable cellulose is present in an amount of up to 1.4% wt. ofthe said composition.
 11. A compressed water-softening compositionaccording to claim 1 wherein the water-swellable cellulose is present inan amount of up to 95% wt. of the blend of disintegrating agents.
 12. Acompressed water-softening composition according to claim 2 herein theblend of disintegrating agents is present in an amount of up to 10% byweight of the composition.
 13. A compressed water-softening compositionaccording to claim 2 wherein the blend of disintegrating agents ispresent in an amount of at least 0.1% by weight of the composition. 14.A compressed water-softening composition according to claim 2 whereinthe water-soluble salt has a solubility of at least 50 g/100 g ofdeionised water at 20° C.
 15. A compressed water-softening compositionaccording to claim 2 wherein the water-swellable cellulose has a wateruptake of at least 15 g of deionised water at 20° C. per g ofwater-swellable cellulose.
 16. A compressed water-softening compositionaccording to claim 2 wherein the water-softening active is selected fromthe group: ion exchange agents, ion capture agents, and anti-nucleatingagents.
 17. A compressed water-softening composition according to claim2 wherein the composition comprises less than 5% by weight of asurfactant or bleach ingredients.
 18. A compressed water-softeningcomposition according to claim 17 wherein the composition comprises lessthan 1% by weight of a surfactant or bleach ingredients.
 19. Acompressed water-softening composition according to claim 18 wherein thecomposition comprises 0% by weight of a surfactant or bleachingredients.